Trace elements such as iron, zinc, cobalt, manganese and molybdenum are known to be necessary for the growth of healthy plants. Frequently they occur in soils, but are in a form not available to the plant. Their availability can be improved by adding certain chelating agents when these metals are present in the soil, but unavailable to plants. These metals then form chelates which are then able to be taken up by the plant. When the elements are not present in the soil, they can be added as their chelates.
Some of the most widely used of chelating agents are chelates of carboxylated and hydroxyalkylated amines, e.g., ethylenediaminetetraacetic acid, monoethanolethylenediaminetriacetic acid, diethylenetriaminepentacetic acid and the like. A description of preparing such chelates and their use in agriculture can be found in U.S. Pat. No. 3,051,563. The use of chelates is also described in U.S. Pat. No. 3,091,522.
One of the chelating agents, available commercially, for use in supplying manganese is a chelate of disodium ethylenediaminetetraacetic acid (EDTA (Na).sub.2) with manganese. It is supplied as an aqueous solution which contains 5% manganese by weight. This particular product, while giving satisfactory results with respect to supplying manganese to plants when applied to soil, nevertheless has poor storage properties in that it has a tendency to form a precipitate after undergoing numerous freeze-thaw cycles. This precipitates out some of the manganese, making the remaining solution less concentrated. In addition, the precipitate plugs up the apparatus used to dispense it. This is a disadvantage when it is stored for use under climatic conditions in which the temperature often fluctuates from above to below its freezing point.
It has now been discovered that a product which contains certain amounts of N-hydroxyethylethylenediaminetriacetic acid (HEDTA(H).sub.3) as the chelant for manganese along with the EDTA(Na).sub.2 is not affected by freeze-thaw cyclic conditions and no precipitate forms.